Drive unit with limited slip and driveline disconnect capability

ABSTRACT

A clutch assembly includes a first clutch assembly having first clutch plates rotatably fixed to a first shaft and first carrier plates rotatably fixed to a clutch basket. The clutch assembly further includes a second clutch assembly having second clutch plates rotatably fixed to a second shaft and second carrier plates rotatably fixed to the clutch basket. The first and second clutch assemblies rotate about a common central axis and are actuated by a common actuator.

TECHNICAL FIELD

This disclosure relates to a clutch assembly and more particularly to asecondary axle clutch assembly having torque transfer capabilities andlimited slip differential capabilities actuated by a single actuator.

BACKGROUND

A motor vehicle may be provided with an all-wheel-drive (AWD) powertraincapable of transmitting power to the wheels of a primary axle and to thewheels of a secondary axle. Power is provided to the secondary axlethrough a rear drive unit having a differential assembly. Variousdifferential assemblies may be utilized, including open, limited slip,and locking differentials. Open differentials have a gear train thatallows the output shafts of the differential to spin at different speedswhile maintaining the sum of their speeds proportional to the input ofthe differential, but the amount of torque transferred to the inner andouter wheels must be equal. A limited slip differential allows differentamounts of torque to be transferred to the inner-wheel compared to theouter-wheel during a turn.

AWD systems tend to degrade vehicle fuel economy due to increaseddriveline parasitic losses even when AWD is not activated. Theseparasitic losses occur, in part, because the secondary drive wheels andtheir rotation cause a drag torque to be exerted on the driving element.An AWD vehicle may be provided with a driveline disconnect system thatimproves fuel economy by disconnecting parts of the driveline when AWDis not activated. In many aspects, this is accomplished with a sidemounted clutch on a rear drive unit that functions as a torquetransfer/disconnect device. In many instances, inclusion of a drivelinedisconnect system in a side clutch rear drive unit precludes the use ofa mechanical limited slip differential in the rear drive unit.

SUMMARY

This disclosure relates to a clutch assembly having torque transfercapabilities and limited slip differential capabilities actuated by asingle actuator. In some approaches, a secondary axle clutch assemblyincludes a differential carrier having a differential shaft rotatableabout a central axis of rotation. A plurality of limited slipdifferential (LSD) clutch plates are rotatably fixed to the differentialshaft and are axially movable relative to the differential shaft. Anintermediate shaft extends coaxially with the differential shaft and isrotatable about the central axis of rotation. A plurality of torqueclutch plates are rotatably fixed to the intermediate shaft and areaxially movable relative to the intermediate shaft. A clutch basketextends over the torque clutch plates and the LSD clutch plates and isrotatable about the central axis of rotation. The clutch basket includesa first plurality of carrier plates disposed adjacent to the torqueclutch plates and a second plurality of carrier plates disposed adjacentto the LSD clutch plates. An actuator is adapted to apply an axial forceto the torque clutch plates and the LSD clutch plates to engage thetorque clutch plates with the first plurality of carrier plates, and toengage the LSD clutch plates with the second plurality of carrierplates.

In some approaches, a clutch assembly includes a first clutch assemblyhaving first clutch plates rotatably fixed to a first shaft and firstcarrier plates rotatably fixed to a clutch basket. The clutch assemblyfurther includes a second clutch assembly having second clutch platesrotatably fixed to a second shaft and second carrier plates rotatablyfixed to the clutch basket. The first and second clutch assembliesrotate about a common central axis and are actuated by a commonactuator.

In still other approaches, a method of actuating multiple clutchassemblies includes axially displacing, using a common actuator, a firstplurality of clutch plates rotationally fixed to a first shaft. Themethod further includes axially displacing, using the common actuator, asecond plurality of clutch plates rotationally fixed to a second shaft.The first shaft is coaxial with the second shaft and extends at leastpartially within the second shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a vehicle powertrain.

FIG. 2 is a schematic diagram showing a rear drive unit.

FIG. 3 is a schematic diagram showing a rear drive unit in a firststage.

FIG. 4 is a schematic diagram showing the rear drive unit of FIG. 3 in asecond stage.

FIG. 5 is a schematic diagram showing the rear drive unit of FIG. 3 in athird stage.

FIG. 6 is cross-sectional view of a rear drive unit having a ball rampactuator.

FIGS. 7a and 7b are example clutch engagement profiles for a ball rampactuator.

FIG. 8 is a schematic diagram showing a double ball ramp actuator.

FIG. 9 is a perspective view of a double ball ramp actuator.

FIG. 10 is a perspective view of a double ball ramp actuator havingcages.

FIG. 11 is a front elevational view of a double ball ramp actuator.

FIG. 12 is a side elevational view of a double ball ramp actuator.

FIG. 13 is a side elevational view of a double ball ramp actuator havinga pressure plate with projections.

FIG. 14 is a front elevational view of a double ball ramp actuatorhaving a pressure plate with projections.

FIGS. 15a-15e are example ramp profiles for a double ball ramp actuator.

FIG. 16 is a schematic diagram showing a double ball ramp actuatorhaving rings axially movable in opposite directions.

FIG. 17 is a chart showing example axial displacements of inner andouter rings.

FIG. 18 is an exploded side elevational view of a rear drive unit havinga double ball ramp actuator.

FIG. 19 is a side elevational view of the rear drive unit of FIG. 18.

FIGS. 20a and 20b are example clutch engagement profiles for a doubleball ramp actuator.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

Referring to FIGS. 1 and 2, the powertrain of a motor vehicle 10includes an engine 12, such as an internal combustion engine; atransaxle 13 for producing multiple forward drive speed ratios andreverse drive; halfshafts 14, 16 for transmitting rotating power betweenthe transaxle's output and the front driven wheels 18, 20; a rear driveunit (RDU) 22; a driveshaft 24; a power transfer unit (PTU) 26 fortransmitting rotating power between the transaxle's output and thedriveshaft; and a clutch assembly 28 for providing limited slipcapabilities and for connecting and disconnecting the output of the RDUand the rear driven wheels 30, 32.

As shown in FIG. 2, the RDU 22 includes a differential carrier 34.Inside the differential carrier 34 are a differential side gear 36,which is connected by a shaft 40 to wheel 30, and a differential sidegear 38, which is connected by a shaft 42 to wheel 32. The differentialassembly of the RDU 22 is, for example, a limited slip differential(LSD), and preferably an electronic limited slip differential (eLSD).Where an eLSD is utilized, the eLSD is controlled by at least onecontroller 44 (shown in FIG. 1), computer, or other such network ofinterconnected controllers in a control system. The eLSD controls theamount of clamping force applied in a clutch pack, as described ingreater detail elsewhere herein. This provides a computerized control ofthe clutch pressure in order to selectively deliver various amounts oftorque to the wheels 30, 32.

Although described herein in conjunction with a rear drive unit, it isexpressly contemplated that the clutch assembly and/or the clutchactuator may be incorporated in a front drive unit, along thedriveshaft, or in any other suitable region of a vehicle.

Referring to FIG. 3, a ring gear 46 secured to the differential carrier34 receives a torque input from an input pinion 48. The input pinion 48is connected to a companion flange (not shown), which in turn isconnected to a driveshaft (e.g., driveshaft 24 in FIG. 1) that transmitsoutput torque from a power transfer unit (e.g., PTU 26 in FIG. 1),transmission, or transfer case to the RDU 22. Differential pinion gears50, 52 are driveably connected to the differential carrier 34 by a pin54 and are in continuous meshing engagement with the differential sidegears 36, 38.

The differential carrier 34 includes a differential shaft 56 thatextends into a clutch basket 58. An intermediate shaft 60 extends fromthe differential side gear 38 into the clutch basket 58. Theintermediate shaft 60 extends coaxially with the differential shaft 56,and both are rotatable about the central axis of rotation 62. In apreferred approach, shown in FIG. 3, the intermediate shaft 60 has anouter diameter less than an inner diameter of the differential shaft 56,and at least a portion of the intermediate shaft 60 is disposed withinand extends through at least a portion of the differential shaft 56.Other suitable configurations of the intermediate shaft 60 relative tothe differential shaft 56 are possible.

The clutch assembly 28 includes a clutch basket 58 that houses a torquetransfer clutch assembly 64 and an LSD clutch assembly 66. The torquetransfer clutch assembly 64 and the LSD clutch assembly 66 are coaxialand rotate about a common central axis 62. In some approaches, thetorque transfer clutch assembly 64 and the LSD clutch assembly 66 areimmediately adjacent. In other approaches, the torque transfer clutchassembly 64 and the LSD clutch assembly 66 are adjacent and separated bya separator plate 76. Other coaxial arrangements are expresslycontemplated.

The torque transfer clutch assembly 64 includes torque transfer clutchplates 68 that are coupled to a differential side gear (e.g.,differential side gear 38) through the intermediate shaft 60. The torquetransfer clutch plates 68 are preferably friction plates, but may alsobe steel plates (e.g., pressure plates) or combinations thereof, and maybe formed of any suitable material. The torque transfer clutch plates 68are rotatably fixed to the intermediate shaft 60 such that rotation ofthe intermediate shaft 60 causes corresponding rotation of the torquetransfer clutch plates 68. The torque transfer clutch plates 68 are alsoaxially movable relative to the intermediate shaft 60. In a preferredapproach, the torque transfer clutch plates 68 are internally splined tothe intermediate shaft 60. For example, a series of protrusions andrecesses disposed at an interior diameter of the torque transfer clutchplates 68 may mesh with a corresponding series of protrusions andrecesses disposed at an exterior diameter of the intermediate shaft 60.In this way, the torque transfer clutch plates 68 and the intermediateshaft 60 may be in continuous meshed engagement.

The torque transfer clutch assembly 64 also includes torque transfercarrier plates 70 that are coupled to the clutch basket 58. The torquetransfer carrier plates 70 are preferably steel plates (e.g., pressureplates), but may also be friction plates or combinations thereof, andmay be formed of any suitable material. The torque transfer carrierplates 70 are rotatably fixed to the clutch basket 58 such that rotationof the torque transfer carrier plates 70 causes corresponding rotationof the clutch basket 58. The torque transfer carrier plates 70 are alsoaxially movable relative to the clutch basket 58. In a preferredapproach, the torque transfer carrier plates 70 are externally splinedto the clutch basket 58. For example, a series of protrusions and recessdisposed at an exterior diameter of the torque transfer carrier plates70 may mesh with a corresponding series of protrusions and recessdisposed at an interior surface of the clutch basket 58. In anotherexample, the torque transfer carrier plates 70 include one or moreprotrusions, and the clutch basket 58 includes one or more recesses orapertures adapted to receive the one or more protrusions.

Thus, when the torque transfer clutch plates 68 engage the torquetransfer carrier plates 70, torque is transferred from the intermediateshaft 60 to the clutch basket 58 through the engaged torque transferclutch plates 68 and torque transfer carrier plates 70. As the clutchbasket 58 is rotatably coupled to the output shaft 42, torque is alsodirectly transferred to the rear wheel 32. When the torque transferclutch plates 68 disengage from the torque transfer carrier plates 70,the differential carrier 34 is disconnected and the rear wheel 32 istherefore disconnected from the powertrain of the vehicle 10. As such,the torque transfer clutch assembly 64 is capable of providing“disconnect” capabilities.

The LSD clutch assembly 66 includes LSD clutch plates 72 that arecoupled to the differential carrier 34 through the differential shaft56. The LSD clutch plates 72 are preferably friction plates, but mayalso be steel plates (e.g., pressure plates) or combinations thereof,and may be formed of any suitable material. The LSD clutch plates 72 arerotatably fixed to the differential shaft 56 such that rotation of thedifferential shaft 56 causes corresponding rotation of the LSD clutchplates 72. The LSD clutch plates 72 are also axially movable relative tothe differential shaft 56. In a preferred approach, the LSD clutchplates 72 are internally splined to the differential shaft 56. Forexample, a series of protrusions and recesses disposed at an interiordiameter of the LSD clutch plates 72 may mesh with a correspondingseries of protrusions and recesses disposed at an exterior diameter ofthe differential shaft 56. In this way, the LSD clutch plates 72 and thedifferential shaft 56 may be in continuous meshed engagement.

The LSD clutch assembly 66 also includes LSD carrier plates 74 that arecoupled to the clutch basket 58. The LSD carrier plates 74 arepreferably steel plates (e.g., pressure plates), but may also befriction plates or combinations thereof, and may be formed of anysuitable material. The LSD carrier plates 74 are rotatably fixed to theclutch basket 58 such that rotation of the LSD carrier plates 74 causescorresponding rotation of the clutch basket 58. The LSD carrier plates74 are also axially movable relative to the clutch basket 58. In apreferred approach, the LSD carrier plates 74 are externally splined tothe clutch basket 58. For example, a series of protrusions and recessesdisposed at an exterior diameter of the LSD carrier plates 74 may meshwith a corresponding series of protrusions and recesses disposed at aninterior of the clutch basket 58. In another example, the LSD carrierplates 74 include one or more protrusions, and the clutch basket 58includes one or more recesses or apertures adapted to receive the one ormore protrusions.

Thus, when the LSD clutch plates 72 engage the LSD carrier plates 74,torque is transferred from the differential shaft 56 to the clutchbasket 58 through the engaged LSD clutch plates 72 and LSD carrierplates 74. As the clutch basket 58 is rotatably coupled to the outputshaft 42, the torque is also directly transferred to the rear wheel 32.As such, the LSD clutch assembly 66 is capable of providing “limitedslip” capabilities. As will be appreciated, the torque provided by theLSD clutch assembly 66 may be in addition to, or in place of, the torqueapplied by the torque transfer clutch assembly 64.

The torque transfer clutch assembly 64 and the LSD clutch assembly 66may be separately activated by one or more actuators. FIG. 3 shows aclutch assembly 28 in which neither the torque transfer clutch assembly64 nor the LSD clutch assembly 66 are activated. In this state, the RDU22 does not apply torque to the rear wheels 30, 32 of the vehicle 10.

FIG. 4 shows a clutch assembly 28 in which the torque transfer clutchassembly 64 has been activated (e.g., by the controller 44 moving amotor to a first motor position), but the LSD clutch assembly 66 has notbeen activated. In this state, the torque transfer clutch plates 68 andthe torque transfer carrier plates 70 are axially moved into engagement,and the RDU 22 applies torque to the rear wheels of the vehicle.However, because the LSD clutch assembly 66 has not been activated, theLSD clutch plates 72 and the LSD carrier plates 74 are not engaged, andthe differential assembly does not provide limited slip capabilities.Rather, the differential components of the RDU 22 continue to performsimilar to that of an open differential. This may be the case, forexample, when the controller 44 determines the vehicle 10 isaccelerating or otherwise requires torque to be applied to the rearwheels 30, 32, but that differential control is unnecessary.

FIG. 5 shows a clutch assembly 28 in which both the torque transferclutch assembly 64 and the LSD clutch assembly 66 are activated (e.g.,by the controller 44 moving a motor to a second motor position). In thisstate, the LSD clutch plates 72 and the LSD carrier plates 74 areaxially moved into engagement, and the RDU 22 applies additional torqueto the rear wheels of the vehicle. In this way, the differentialcomponents of the RDU 22 perform similarly to that of a lockeddifferential. This may be the case, for example, when the controller 44determines the vehicle 10 is accelerating or otherwise requires torqueto be applied to the rear wheels 30, 32, and that differential controlis required, for example, upon detecting decreased traction in one ofthe wheels.

In some aspects, the LSD clutch assembly 66 may be activated prior toactivation of the torque transfer clutch assembly 64. Preliminaryactivation of the LSD clutch assembly 66 may result in a torquetransfer; however, the torque applied may be at a very high resolution.Such high resolution may be preferable, for example, when the controller44 attempts to modulate the speed of the driveshaft 24 during anengagement event.

The torque transfer clutch assembly 64 and the LSD clutch assembly 66are preferably actuated by a single, common actuator. Referring now toFIG. 6, the actuator may be a ball ramp actuator 78 capable ofseparately activating the torque transfer clutch assembly 64 and the LSDclutch assembly 66. The ball ramp actuator 78 includes a stationaryplate or ring 80, a ring 82 rotatable about a central axis 62, and atleast one ball 84 disposed between the stationary ring 80 and rotatablering 82. Rotation of the rotatable ring 82, caused for example, by thecontroller 44 actuating the actuator, causes the balls 84 to travelthrough grooves in the stationary ring 80 and rotatable ring 82. Due tothe profiles of the grooves, as the rotatable ring 82 rotates, the balls84 cause the rotatable ring 82 to translate axially away from thestationary ring 80 and toward the torque transfer clutch assembly 64 andthe LSD clutch assembly 66. The rotatable ring 82 urges the torquetransfer clutch assembly 64 and the LSD clutch assembly 66 intoengagement, preferably through a thrust bearing or pressure plate 86. Insome approaches, the stationary ring is rotatable about the centralaxis, but does not translate axially along the central axis.

The ball ramp actuator 78 may include a first set of wave springs 88adjacent to the torque transfer carrier plates 70 and/or a second set ofwave springs 90 adjacent to the LSD carrier plates 74. The second set ofwave springs 90 preferably have a greater stiffness than the first setof wave springs 88. In this way, axial displacement of the rotatablering 80 as the motor moves to a first motor position urges the torquetransfer clutch assembly 64 into engagement, while the second set ofwave springs 90 keeps the LSD clutch assembly 66 out of engagement.Further axial displacement of the rotatable ring 80 as the motor movesto a second motor position subsequently overcomes the stiffness of thesecond set of wave springs 90 and urges the LSD clutch assembly 66 intoengagement. Offsetting the engagements of torque transfer clutchassembly 64 and the LSD clutch assembly 66 may be controlled byproviding first and/or second set of wave springs 88, 90 having variousstiffnesses.

Example clutch engagement profiles for the ball ramp actuator 78 areshown in FIGS. 7a and 7b . The drive torque, or propulsive torque,represents the amount of toque on the driveshaft. The LSD torque is themaximum achievable torque difference between the two wheels. The LSDtorque may be, for example, about one-third of the drive torque. In theclutch engagement profile shown in FIG. 7a , torque is transferredthrough both the torque transfer clutch assembly 64 and the LSD clutchassembly 66 at a first motor position. In the clutch engagement profileshown in FIG. 7b , torque is transferred through the torque transferclutch assembly 64 at a first motor position, while no torque istransferred through the LSD clutch assembly 66 at the first motorposition. At a second motor position, torque is transferred through boththe torque transfer clutch assembly 64 and the LSD clutch assembly 66.This may be desirable, for example, to improve driveshaftsynchronization control.

In addition to a ball ramp actuator, other actuators may be used toactuate the torque transfer clutch assembly 64 and the LSD clutchassembly 66, such as one or more pistons, solenoids, motors, or othersuitable hydraulic, pneumatic, electric, thermal, magnetic, ormechanical actuators.

Referring now to FIG. 8, a double ball ramp actuator 100 may be used toprovide multiple-stage activation. More specifically, a double ball rampactuator 100 may be used to provide two stage actuation of the torquetransfer clutch assembly 64 and the LSD clutch assembly 66 using anouter ring 102 and an inner ring 104, respectively.

As shown in FIGS. 9-11, the double ball ramp actuator 100 includes adrive gear 106 that is selectively rotated by a motor 108. The drivegear 106 is engaged with an exterior surface of the outer ring 102, forexample, through a gear teeth arrangement. In this way, as the motor 108rotates the drive gear 106, the drive gear 106 causes the outer ring 102to rotate. In some approaches, the double ball ramp actuator 100 furtherincludes a stationary ring 110 and, in still other approaches, apressure plate 112. In this way, the outer ring 102 and inner ring 104may be disposed between the stationary ring 110 and pressure plate 112.

As shown in FIG. 12, the pressure plate 112 may have a continuous faceor side surface. In another approach, shown in FIGS. 13 and 14, thepressure plate 112 includes a plurality of fingers or projections 113projecting from the face or side surface.

The outer ring 102 has at least one outer depression or groove, andpreferably four outer ring grooves 114 disposed on a face of the outerring 102. As shown in FIG. 11, and discussed in greater detail elsewhereherein, the outer ring grooves 114 have first-stage ramp profiles 114 aand second-stage ramp profiles 114 b. Balls or bearings 116 are disposedin the outer ring grooves 114 and in corresponding outer grooves 118 ofthe stationary ring 110 and traverse between the first- and second-stageramp profiles 114 a, 114 b. In some approaches, the outer grooves 118 ofthe stationary ring 110 have groove profiles instead of, or in additionto, the first- and second-stage ramp profiles 114 a, 114 b of the outerring 102.

The inner ring 104 similarly has at least one inner groove ordepression, and preferably four inner ring grooves 120 disposed on aface of the inner ring 104. The inner ring grooves 120 have first-stageramp profiles 120 a and second-stage ramp profiles 120 b. Balls orbearings 122 are disposed in the inner ring grooves 120 and incorresponding inner grooves 124 of the stationary ring 110 and traversebetween the first- and second-stage ramp profiles 120 a, 120 b. In someapproaches, the inner grooves 124 of the stationary ring 110 have grooveprofiles instead of, or in addition to, the first- and second-stage rampprofiles 120 a, 120 b of the inner ring 104.

Referring momentarily to FIG. 10, the double ball ramp actuator 100 mayinclude an outer cage 126 disposed between the outer ring 102 and thestationary ring 110, and an inner cage 128 disposed between the innerring 104 and the stationary ring 110. Outer cage 126 includes aplurality of holes 130 spaced circumferentially around axis 62. Theholes 130 correspond to and fit over the outer balls 116. Inner cage 128similarly includes a plurality of holes 132 spaced circumferentiallyaround central axis 62. The holes 132 correspond to and fit over theinner balls 122. Cages 126, 128 act to maintain consistent spacingbetween balls 116, 122 as the balls rotate about the central axis 62.

The inner ring 104 is engaged with the outer ring 102 such that rotationof the outer ring 102 causes a corresponding rotation of the inner ring104. This is preferably achieved by engaging an exterior surface of theinner ring 104 with an interior surface of the outer ring 102. In oneapproach, shown in FIGS. 9-11, the interior surface of the outer ring102 includes at least one slot 134, and an exterior surface of the innerring 104 includes at least one key or protrusion 136 sized to engage theslot. In another approach, shown in FIG. 14, an interior surface of theouter ring 102 includes a first plurality of teeth 138, and an exteriorsurface of the inner ring 104 includes a second plurality of teeth 140adapted to engage the first plurality of teeth. In either approach,rotational movement of the inner ring 104 relative to the outer ring 102is inhibited.

Although relative rotational movement is inhibited, the double ball rampactuator 100 provides uncoupled axial translation of the outer ring 102relative to the inner ring 104, and vice-versa. In this way, the doubleball ramp actuator 100 permits separate and distinct axial movement ofthe two rings along the central axis 62.

In use, the motor 108 turns the drive gear 106, thereby rotating theouter ring 102. Because the inner ring 104 is splined to the outer ring102, rotation of the outer ring 102 causes corresponding rotation of theinner ring 104. As the rings rotate, at least one of the outer ring 102and the inner ring 104 is able to translate or move axially along thecentral axis 62 relative to the other ring. In a preferred approach, theouter ring 102 and inner ring 104 are able to separately translate alongthe central axis 62. For example, as will be discussed in greater detailelsewhere herein, the outer ring 102 may translate at a first time(based, for example, on motor position) while the inner ring 104 remainsstationary; the inner ring 104 may translate at a second time (based,for example, on motor position) while the outer ring 102 remainsstationary; the inner ring 104 may translate at a first time while theouter ring 102 remains stationary; the outer ring 102 may translate at asecond time while the inner ring 104 remains stationary; the outer ring102 and the inner ring 104 may translate at the same time and atdifferent rates; or the outer ring 102 and the inner ring 104 maytranslate at the same time and in different axial directions. Othercombinations of axial movement stages of the outer ring 102 and theinner ring 104 (based, for example, on motor position) are expresslycontemplated herein. Furthermore, while only two concentric rings aredescribed herein, three or more concentric rings may be used to provideadditional functionality. For example, three concentric rings may beprovided, and may have one, two, three, or more profiles stages toprovide additional functionality.

Axial movement of the outer ring 102 and the inner ring 104 may becontrolled by stage ramp profiles of the outer ring grooves 114 of theouter ring 102 and inner ring grooves 120 of the inner ring 104. As usedherein, a ramp profile of a groove refers to the axial depth along alength of the groove. An axial depth of a groove refers to the depth ofthe groove formed in the ring, and may be considered, for example,between opposing side surfaces or faces of the ring and relative tocentral axis 62. A stage refers to a segment of the groove. A groove mayhave, for example, a stage having a constant axial depth, such that thedepth of the groove does not vary along such stage. A groove may alsohave a stage having a varying axial depth. In such a stage, the axialdepth increases or decreases along a length of the stage of the groove.Although one or two groove stages are described herein, rings may beprovided with grooves having three or more groove stages to provideadditional functionality.

Referring now to FIG. 15a , a double ball ramp actuator 100 may includean outer ring 102 provided with outer ring grooves 114 having afirst-stage ramp profile having a varying axial depth and a second-stageramp profile having a constant axial depth. The double ball rampactuator 100 may also include an inner ring 104 provided with inner ringgrooves 120 having a first-stage ramp profile having a constant axialdepth and a second-stage ramp profile having a varying axial depth. Inthis approach, as the rings rotate through the first stage, the outerballs 116 travel through the varying axial depth profiles of the outerring grooves 114, thereby increasingly urging the outer ring 102 awayfrom the stationary ring 110. In this way, the outer ring 102 is axiallydisplaced during the first stage. The inner balls 122 travel through theconstant axial depth profiles of the inner ring grooves 120 during thefirst stage, and thus do not urge the inner ring 104 away from thestationary ring 110. In this way, the inner ring 104 is not axiallydisplaced during the first stage. As the rings rotate through the secondstage, the outer balls 116 travel through the constant axial depthprofiles of the outer ring grooves 114, and thus do not urge the outerring 102 away from the stationary ring 110. In this way, the outer ring102 is not axially displaced during the second stage. The inner balls122 travel through the varying axial depth profiles of the inner ringgrooves 120 during the second stage, thereby increasingly urging theinner ring 104 away from the stationary ring 110. In this way, the innerring 104 is axially displaced during the second stage.

Referring now to FIG. 15b , a double ball ramp actuator 100 may includean outer ring 102 provided with outer ring grooves 114 having afirst-stage ramp profile having a constant axial depth and asecond-stage ramp profile having a varying axial depth. The double ballramp actuator 100 may also include an inner ring 104 provided with innerring grooves 120 having a first-stage ramp profile having a varyingaxial depth and a second-stage ramp profile having a constant axialdepth. In this approach, as the rings rotate through the first stage,the outer balls 116 travel through the constant axial depth s of theouter ring grooves 114, and thus do not urge the outer ring 102 awayfrom the stationary ring 110. In this way, the outer ring 102 is notaxially displaced during the second stage. The inner balls 122 travelthrough the varying axial depth profiles of the inner ring grooves 120during the first stage, thereby increasingly urging the inner ring 104away from the stationary ring 110. In this way, the inner ring 104 isaxially displaced during the first stage. As the rings rotate throughthe second stage, the outer balls 116 travel through the varying axialdepth profiles of the outer ring grooves 114, thereby increasinglyurging the outer ring 102 away from the stationary ring 110. In thisway, the outer ring 102 is axially displaced during the second stage.The inner balls 122 travel through the constant axial depth profiles ofthe inner ring grooves 120 during the second stage, and thus do not urgethe inner ring 104 away from the stationary ring 110. In this way, theinner ring 104 is not axially displaced during the second stage.

As shown in FIGS. 15a and 15b , ramp profiles grooves 114, 120 of theouter ring 102 and inner ring 104 may be coordinated such thattransitions between stages occur concurrently. In another approach, thetransitions between stages of the rings may be offset. For example, asshown in FIG. 15c , the grooves 120 of the inner ring 104 may beprovided with ramp profiles that transition (e.g., based on motorposition) between a first stage and a second stage prior to rampprofiles of the grooves 114 of the outer ring 102 transitioning betweena first stage and a second stage. In other approaches, the grooves 120of the inner ring 104 may be provided with ramp profiles that transitionbetween a first stage and a second stage after ramp profiles of thegrooves 114 of the outer ring 102 transition between a first stage and asecond stage.

In still another approach, a double ball ramp actuator 100 may includean outer ring 102 provided with outer ring grooves 114 having a singlestage profile, and an inner ring 104 provided with inner ring grooves120 having a single profile. In this approach, the outer ring grooves114 may have a first slope gradient, and the inner ring grooves 120 mayhave a second slope gradient different than the first slope gradient.For example, as shown in FIG. 15d , the slope gradient of the outer ringgrooves 114 may effect axial movement of the outer ring 102 at a greaterrate (e.g., as determined by motor position) than the rate at which theslope gradient of the inner ring grooves 120 effects axial movement ofthe inner ring 104. Alternatively, the slope gradient of the outer ringgrooves 114 may effect axial movement of the outer ring 102 at a slowerrate than the rate at which the slope gradient of the inner ring grooves120 effects axial movement of the inner ring 104.

In still another approach, shown in FIG. 15e , a double ball rampactuator 100 may include an outer ring 102 provided with outer ringgrooves 114 having a positive profile stage, and an inner ring 104provided with inner ring grooves 120 having a negative profile stage. Inthis way, as shown in FIG. 16, the outer ring 102 may be urged in afirst axial direction during rotation of the rings, and the inner ring104 may be urged in a second axial direction opposite the first axialdirection. Opposite axial movement of the two rings may occurconcurrently, or may occur at separately and distinctly based on motorposition.

As shown in FIG. 17, a double ball ramp actuator 100 may separatelyaxially displace an outer ring 102 and an inner ring 104 to achievedistinct displacements at a given time (e.g., based on a motorposition). In this way, the double ball ramp actuator 100 acts as amulti-stage ball ramp actuator. This arrangement permits two axialdisplacements using only a single actuator. Thus, only a single motor isnecessary to achieve the multiple stages. Furthermore, the double ballramp actuator 100 may be sized and dimensioned to occupy the same spaceas conventional ball ramp actuators. The sloped grooves can be designedto coordinate the relative movement between the outer and inner ramps102, 104 depending on the desired application. Furthermore, the doubleball ramp actuator 100 may be able to convert rotary motion into axialdisplacement with very high force amplification, e.g., 100:1 or greater.

One application for a double ball ramp actuator 100 is shown in FIGS. 18and 19. In this approach, the double ball ramp actuator 100 is capableof providing separate, uncoupled axial displacement of a torque transferclutch assembly 64 and an LSD clutch assembly 66. As shown in FIG. 18,the outer ring 102 axially displaces and imparts an axial force on athrust bearing 142 (e.g., a needle bearing), which imparts an axialforce on the pressure plate 112. The inner ring 104 axially displacesand imparts an axial force on a thrust bearing 144 (e.g., a needlebearing), which imparts an axial force on the LSD clutch assembly 66. Insome approaches (not shown), a pressure plate is disposed between thethrust bearing 144 and the LSD clutch assembly.

In the approach shown in FIGS. 18 and 19, the torque transfer clutchplates 68 are wave springs that are rotatably fixed to the intermediateshaft and axially movable relative to the intermediate shaft. Similarly,the LSD clutch plates 72 are wave springs that are rotatably fixed tothe differential shaft and axially movable relative to the differentialshaft.

Example clutch engagement profiles for the double ball ramp actuator 100are shown in FIGS. 20a and 20b . In the clutch engagement profile shownin FIG. 20a , torque is transferred first through the torque transferclutch assembly 64. At a given motor position, the driveline operates ina traditional eLSD manner, and torque is applied as required through theLSD clutch assembly 66. In this approach, the two clutch assemblies areoperated separately and sequentially. In the clutch engagement profileshown in FIG. 20b , torque is transferred first through the torquetransfer clutch assembly 64. At a given motor position, torque istransferred through both the torque transfer clutch assembly 64 and theLSD clutch assembly 66. At still another motor position, torque isapplied as required through the LSD clutch assembly 66. In thisapproach, the two clutch assemblies are operated separately and, atleast at a given motor position, concurrently.

In this way, a torque transfer clutch assembly 64 and an LSD clutchassembly 66 may be provided in a common clutch basket and may beactivated by a single, common actuator. The arrangements describedherein allow for both disconnect and limited slip capabilities in apackage similar in size to traditional RDU package sizes. Minimizing thenumber of required actuators further reduces weight and cost as comparedto traditional RDUs.

Although described herein in conjunction with vehicle clutches, it isexpressly contemplated that the double ball ramp actuator 100 may beincorporated in other suitable applications in which multiple-stageactuation may be advantageous.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A secondary axle clutch assembly comprising: a differential carrier including a differential shaft rotatable about a central axis of rotation; a plurality of limited slip differential (LSD) clutch plates rotatably fixed to the differential shaft and axially movable relative to the differential shaft; an intermediate shaft extending coaxially with the differential shaft and rotatable about the central axis of rotation; a plurality of torque clutch plates rotatably fixed to the intermediate shaft and axially movable relative to the intermediate shaft; a clutch basket extending over the torque clutch plates and the LSD clutch plates and rotatable about the central axis of rotation, the clutch basket comprising a first plurality of carrier plates disposed adjacent to the torque clutch plates and a second plurality of carrier plates disposed adjacent to the LSD clutch plates; and an actuator adapted to apply an axial force to the torque clutch plates and the LSD clutch plates to engage the torque clutch plates with the first plurality of carrier plates, and to engage the LSD clutch plates with the second plurality of carrier plates.
 2. The secondary axle clutch assembly of claim 1, wherein the intermediate shaft is rotatably connected to a side gear disposed within the differential carrier, and wherein the intermediate shaft includes at least a portion extending within the differential shaft.
 3. The secondary axle clutch assembly of claim 1, wherein the clutch basket is rotatably secured to an output shaft, and wherein the torque clutch plates engage the first plurality of carrier plates to transmit torque from the intermediate shaft to the output shaft through the clutch basket.
 4. The secondary axle clutch assembly of claim 1, wherein the clutch basket is rotatably secured to an output shaft, and wherein the LSD clutch plates engage the second plurality of carrier plates to transmit torque from the differential shaft to the output shaft through the clutch basket.
 5. The secondary axle clutch assembly of claim 1, wherein the torque clutch plates and the LSD clutch plates are coaxial friction plates, and wherein the first plurality of carrier plates and the second plurality of carrier plates are coaxial steel plates.
 6. The secondary axle clutch assembly of claim 1, wherein the actuator is adapted to apply a first axial force to the torque clutch plates to engage the torque clutch plates with the first plurality of carrier plates while the LSD clutch plates are disengaged from the second plurality of carrier plates.
 7. The secondary axle clutch assembly of claim 1, wherein the actuator is adapted to apply a second axial force to the LSD clutch plates to engage the LSD clutch plates with the second plurality of carrier plates while the torque clutch plates are engaged with the second plurality of carrier plates.
 8. The secondary axle clutch assembly of claim 1, further comprising a separator plate disposed between the torque clutch plates and first plurality of carrier plates and the LSD clutch plates and second plurality of carrier plates.
 9. The secondary axle clutch assembly of claim 1, further comprising a first plurality of separator springs disposed between the torque clutch plates and the first plurality of carrier plates, and a second plurality of separator springs disposed between the LSD clutch plates and the second plurality of carrier plates, the second plurality of separator springs having a higher stiffness than the first plurality of separator springs.
 10. The secondary axle clutch assembly of claim 1, wherein the actuator includes only one motor to activate the actuator.
 11. The secondary axle clutch assembly of claim 1, wherein the actuator is selected from the group consisting of a piston and a ball ramp actuator.
 12. The secondary axle clutch assembly of claim 11, wherein the ball ramp actuator is a multiple-stage ball ramp actuator comprising: an axially movable outer ring having at least one outer ring groove and an outer ball disposed in the outer ring groove; an axially movable inner ring rotatably fixed relative to the outer ring, the inner ring having at least one inner ring groove and an inner ball disposed in the inner ring groove; and a pressure plate comprising at least one projection projecting axially from the pressure plate, the pressure plate adapted to apply an axial force to the torque clutch plates when the outer ring is axially displaced, the pressure plate further adapted to apply an axial force to the LSD clutch plates when the inner ring is axially displaced.
 13. A clutch assembly comprising: a first clutch assembly including first clutch plates rotatably fixed to a first shaft and first carrier plates rotatably fixed to a clutch basket; a second clutch assembly including second clutch plates rotatably fixed to a second shaft and second carrier plates rotatably fixed to the clutch basket; and wherein the first and second clutch assemblies rotate about a common central axis and are actuated by a common actuator.
 14. The clutch assembly of claim 13, wherein the first shaft is coaxial with the second shaft and includes at least a portion extending within the second shaft.
 15. The clutch assembly of claim 13, wherein the common actuator effects a first axial displacement of the first clutch assembly prior to effecting a second axial displacement of the second clutch assembly.
 16. The clutch assembly of claim 13, wherein the common actuator effects a first axial displacement of the first clutch assembly at a first rate, and effects a second axial displacement of the second clutch assembly at a second rate different than the first rate.
 17. The clutch assembly of claim 13, wherein the common actuator is actuated by a single motor.
 18. A method of actuating multiple clutch assemblies comprising: axially displacing, using a common actuator, a first plurality of clutch plates rotationally fixed to a first shaft; and axially displacing, using the common actuator, a second plurality of clutch plates rotationally fixed to a second shaft, the first shaft coaxial with the second shaft and extending at least partially within the second shaft.
 19. The method of claim 18, wherein axially displacing the first plurality of clutch plates rotatably connects, through a clutch basket, an output shaft to an intermediate shaft that is rotatably connected to a side gear disposed within a differential carrier.
 20. The method of claim 18, wherein axially displacing the second plurality of clutch plates rotatably connects, through a clutch basket, an output shaft to a differential carrier. 